1. Field of the Invention
The present invention relates to a producing method of an assembled battery including a plurality of re-chargeable battery cells (secondary batteries) arranged in a predetermined direction, and fastened with a load applied to the battery cells in the arrangement direction.
2. Description of Related Art
A lightweight high-energy density lithium-ion secondary battery, nickel-hydrogen battery or another secondary battery, or an electricity storage element such as a capacitor is used as a battery cell, and an assembled battery formed by connecting plural battery cells in series is used as an electric power supply affording high output, and used as an electric power source for installation in a vehicle, or a power source for a personal computer and a portable terminal. For instance, as an example of an assembled battery for installation in a vehicle, Japanese Patent Application Publication No. 2014-137889 discloses an assembled battery configured by arranging plural battery cells in the same shape constituted by lithium-ion secondary batteries, and connecting respective positive electrode terminals and respective negative electrode terminals of the battery cells in series.
Meanwhile, in an assembled battery mounted in a vehicle such as an automobile, it is supposed that a mounting space for the assembled battery is limited, and the assembled battery is used under vibrational circumstances; thus the assembled battery is assembled by arranging a number of battery cells in a fastened state (i.e., a state in which battery cells are mutually fixed) as described in JP 2014-137889 A, for example. In such a fastened state, a considerable load is applied to the individual battery cells assembled into the assembled battery.
In production of an assembled battery, if plural battery cells are arranged and fastened with a load applied to the battery cells in the arrangement direction thereof, the load causes distortion and deformation in the loading direction to a container (i.e., an outer case body for housing an electrode body thereinside) of every battery cell. Hence, a thickness in an arrangement direction of each battery cell in a state in which the battery cells are fastened with a load applied to the battery cells in a predetermined arrangement direction depends on a thickness of an electrode body inside the container of each battery cell. However, there is usually variation (irregularity) in thickness among the electrode bodies to some extent. If a number of battery cells including electrode bodies having aforementioned variation in thickness are arranged and fastened in a stacking direction, variation in thickness in the arrangement direction occurs among the respective battery cells in the fastened state, and the variation in thickness among the battery cells is accumulated. As a result, produced assembled batteries experience variation in length in the arrangement direction. Such variation in length in the arrangement direction (external dimension) among the assembled batteries causes the following inconveniences: the assembled battery cannot be mounted in a previously prepared mounting space, or a redundant gap remains when the assembled battery is mounted in this mounting space. In addition, there may be caused a disadvantage in designing that requires securing of a greater allowance for a guaranteed performance of an external dimension of the assembled battery in order to accept variation in external dimension thereof (i.e., providing a redundant space around the assembled battery). Hence, in production of an assembled battery, it is preferable to reduce variation in length in the arrangement direction of the assembled battery.